Enhanced visible near-infrared photodiode and non-invasive physiological sensor

ABSTRACT

Embodiments of the present disclosure include a photodiode that can detect optical radiation at a broad range of wavelengths. The photodiode can be used as a detector of a non-invasive sensor, which can be used for measuring physiological parameters of a monitored patient. The photodiode can be part of an integrated semiconductor structure that generates a detector signal responsive to optical radiation at both visible and infrared wavelengths incident on the photodiode. The photodiode can include a layer that forms part of an external surface of the photodiode, which is disposed to receive the optical radiation incident on the photodiode and pass the optical radiation to one or more other layers of the photodiode.

RELATED APPLICATIONS

Any and all applications for which a domestic priority claim isidentified in the Application Data Sheet of the present application arehereby incorporated by reference under 37 CFR 1.57.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a block diagram of an example data collection systemcapable of non-invasively measuring one or more analytes of a patient.

FIG. 2 illustrates an example sensor operation process.

FIG. 3 illustrates an example schematic diagram of a semiconductordevice.

FIG. 4 illustrates a graph of quantum efficiency versus opticalradiation wavelength for various example photodiodes.

DETAILED DESCRIPTION I. Introduction

This disclosure in part describes embodiments of non-invasive methods,devices, and systems for measuring a blood analyte, such as oxygen,carbon monoxide, methemoglobin, total hemoglobin, glucose, proteins,lipids, a percentage thereof (for example, saturation) or for measuringmany other physiologically relevant patient characteristics. Thesecharacteristics can relate, for example, to pulse rate, hydration,trending information and analysis, and the like. In certain embodiments,a non-invasive sensor can interface with tissue at a measurement site,irradiate the tissue, and detect optical radiation after attenuation bythe tissue.

This disclosure in part also describes embodiments of a semiconductordevice, such as a photodiode, for detecting optical radiation at bothvisible and near-infrared wavelengths. The semiconductor device can, forexample, be used as part of a non-invasive sensor to detect visible andnear-infrared wavelengths of optical radiation after attenuation bytissue.

Because individual detectors (for example, individual photodiodes) ofnon-invasive sensors may be responsive to a limited range of wavelengthsof optical radiation, multiple detectors may be used in combination, insome instances, to construct a non-invasive sensor that detects opticalradiation at a broad range of wavelengths of optical radiation. Forexample, it is common to use both an InGaAs photodiode in combinationwith a Si photodiode in order to measure a broader range of wavelengths.However, each additional detector included in a non-invasive sensor canutilize additional space within the sensor and cause the sensor to belarger or more complicated to assemble. Also, having two sensors at twodifferent positions can affect the optical radiation path length of therespective detected optical radiation of each detector. This inherentlyintroduces inaccuracies and may require, for instance, somepost-processing compensation to account for the inaccuracies. Moreover,each additional detector can consume space that may be used in anotherway, such as to increase the size of one or more other detectors so thata stronger signal may be obtained.

In some embodiments, a photodiode is disclosed herein that can detectoptical radiation at a broad range of wavelengths obviating thenecessity for two separate photodiodes as was previously utilized. Thephotodiode can be part of an integrated semiconductor structure that cangenerate a detector signal responsive to optical radiation at bothvisible and infrared wavelengths incident on the photodiode. Thephotodiode can include a window layer that forms part of an externalsurface of the photodiode. The external surface may be disposed toreceive the optical radiation incident on the photodiode and pass theoptical radiation to other layers of the photodiode. Advantageously, incertain embodiments, the thickness of the window layer can be minimizedor the bandgap of the window layer can be maximized, or both, toincrease the transmittance of the window layer for certain wavelengthsof optical radiation and thus the responsiveness of photodiode to thecertain wavelengths of optical radiation. For example, in oneimplementation, the photodiode can be an InGaAs photodiode with thewindow layer having a composition of InAlAs and a relatively thinthickness; this implementation can notably result in a hightransmittance of optical radiation both in the near-infrared wavelengthsand visible wavelengths.

The photodiode of the preceding paragraph can be used, for example, as adetector in a non-invasive sensor. In addition, advantageously, thephotodiode of the preceding paragraph can enable a non-invasive sensorto be constructed which has fewer detectors because the photodiode mayserve to detect optical radiation at wavelengths traditionally detectedusing two or more separate detectors. For example, when the photodiodemay be an enhanced InGaAs photodiode, as described herein, with a windowlayer having a InAlAs composition and a relatively thin thickness, thephotodiode can enable the non-invasive sensor to detect opticalradiation traditionally detected using one Si photodiode and onetraditional InGaAs photodiode with a window layer having a InPcomposition and a relatively thicker thickness of about 500 nm. As aresult, the non-invasive sensor constructed in accordance with theteachings of this disclosure may include fewer detectors or the size ofone or more of the detectors can be increased so that the one or moredetectors provide greater signal strength. In one example, the surfacearea covered by the enhanced InGaAs photodiode within the non-invasivesensor can be doubled because the Si photodiode may not be includedwithin the non-invasive sensor, thereby allowing the signal strength ofa detector signal output by the enhanced InGaAs photodiode to be doubledover that of the traditional InGaAs photodiode when combined with the Siphotodiode.

As used herein, optical radiation at visible wavelengths, in addition tohaving its ordinary meaning, can refer to optical radiation in thevisible spectrum ranging from about 380 nm to about 750 nm.Additionally, as used herein, optical radiation at near-infraredwavelengths, in addition to having its ordinary meaning, can refer tooptical radiation in the near-infrared spectrum ranging from about 750nm to about 1700 nm.

For purposes of summarizing the disclosure, certain aspects, advantagesand novel features have been described herein. It is to be understoodthat not necessarily all such advantages can be achieved in accordancewith any particular embodiment. Thus, the embodiments can be embodied orcarried out in a manner that achieves or optimizes one advantage orgroup of advantages as taught herein without necessarily achieving otheradvantages as can be taught or suggested herein.

II. Patient Monitoring System with Non-Invasive Sensor

FIG. 1 illustrates an example of a data collection system 100. The datacollection system 100 non-invasively can measure a blood analyte, suchas oxygen, carbon monoxide, methemoglobin, total hemoglobin, glucose,proteins, glucose, lipids, a percentage thereof (e.g., saturation) orfor measuring many other physiologically relevant patientcharacteristics. The data collection system 100 can also measureadditional blood analytes or other physiological parameters useful indetermining a state or trend of wellness of a patient.

The data collection system 100 can measure analyte concentrations,including glucose, at least in part by detecting optical radiationattenuated by a measurement site 102. The measurement site 102 can beany location on a patient's body, such as a finger, foot, ear lobe, orthe like. For convenience, this disclosure is described primarily in thecontext of a finger measurement site 102. However, the features of theembodiments disclosed herein can be used with other measurement sites102.

In the depicted embodiment, the data collection system 100 includes anoptional tissue thickness adjuster or tissue shaper 105, which caninclude one or more protrusions, bumps, lenses, or other suitabletissue-shaping mechanisms. In certain embodiments, the tissue shaper 105is a flat or substantially flat surface that can be positioned proximatethe measurement site 102 and that can apply sufficient pressure to causethe tissue of the measurement site 102 to be flat or substantially flat.In other embodiments, the tissue shaper 105 is a convex or substantiallyconvex surface with respect to the measurement site 102.

The data collection system 100 shown also includes an optional noiseshield 103. The noise shield 103 can be adapted to reduceelectromagnetic noise while increasing the transmittance of opticalradiation from the measurement site 102 to one or more detectors 106.For example, the noise shield 103 can advantageously include aconductive coated glass or metal grid electrically communicating withone or more other shields of the sensor 101 or electrically grounded.

The measurement site 102 can be located somewhere along a non-dominantarm or a non-dominant hand, e.g., a right-handed person's left arm orleft hand. In some patients, the non-dominant arm or hand can have lessmusculature and higher fat content, which can result in less watercontent in that tissue of the patient. Tissue having less water contentcan provide less interference with the particular wavelengths that areabsorbed in a useful manner by blood analytes like glucose. Accordingly,in some embodiments, the data collection system 100 can be used on aperson's non-dominant hand or arm.

The data collection system 100 can include a sensor 101 (or multiplesensors) that is coupled to a processing device or physiological monitor109. In some implementations, the sensor 101 and the monitor 109 can beintegrated together into a single unit. In other implementations, thesensor 101 and the monitor 109 can be separate from each other andcommunicate one with another in any suitable manner, such as via a wiredor wireless connection. The sensor 101 and monitor 109 can be attachableand detachable from each other for the convenience of the user orcaregiver, for ease of storage, sterility issues, or the like. Thesensor 101 and the monitor 109 will now be further described.

In the depicted embodiment shown in FIG. 1 , the sensor 101 includes anemitter 104, a set of detectors 106, and a front-end interface 108. Theemitter 104 can serve as the source of optical radiation transmittedtowards the measurement site 102. The emitter 104 can include one ormore sources of optical radiation, such as light-emitting diodes (LEDs),laser diodes, incandescent bulbs with appropriate frequency-selectivefilters, combinations of the same, or the like. In an embodiment, theemitter 104 includes sets of optical sources that are capable ofemitting visible and near-infrared optical radiation.

In some embodiments, the emitter 104 is used as a point optical source,and thus, the one or more optical sources of the emitter 104 can belocated within a close distance to each other, such as within about a 2mm to about 4 mm. The emitter 104 can be arranged in an array, such asis described in U.S. Patent Application Publication No. 2006/0211924,filed Sep. 21, 2006, titled “Multiple Wavelength Sensor Emitters,” thedisclosure of which is hereby incorporated by reference in its entirety.In particular, the emitter 104 can be arranged at least in part asdescribed in paragraphs [0061] through [0068] of the aforementionedpublication, which paragraphs are hereby incorporated specifically byreference. Other relative spatial relationships can be used to arrangethe emitter 104.

The emitter 104 of the data collection system 100 can emit, for example,combinations of optical radiation in various bands of interest. Forinstance, for analytes like glucose, the emitter 104 can emit opticalradiation at three (3) or more wavelengths between about 1600 nm toabout 1700 nm. Measurements at these wavelengths can be advantageouslyused to compensate or confirm the contribution of protein, water, andother non-hemoglobin species exhibited in measurements for analytes likeglucose conducted between about 1600 nm and about 1700 nm. Of course,other wavelengths and combinations of wavelengths can be used to measureanalytes or to distinguish other types of tissue, fluids, tissueproperties, fluid properties, combinations of the same or the like.

The emitter 104 can emit optical radiation across other spectra forother analytes. In particular, the emitter 104 can employ opticalradiation wavelengths to measure various blood analytes or percentages(e.g., saturation) thereof. For instance, the emitter 104 can emitoptical radiation in the form of pulses at wavelengths about 905 nm,about 1050 nm, about 1200 nm, about 1300 nm, about 1330 nm, about 1610nm, about 1640 nm, and about 1665 nm. In another embodiment, the emitter104 can emit optical radiation ranging from about 860 nm to about 950nm, about 950 nm to about 1100 nm, about 1100 nm to about 1270 nm, about1250 nm to about 1350 nm, about 1300 nm to about 1360 nm, and about 1590nm to about 1700 nm. Of course, the emitter 104 can transmit any of avariety of wavelengths of visible or near-infrared optical radiation.

The data collection system 100 also includes a driver 111 that drivesthe emitter 104. The driver 111 can be a circuit or the like that iscontrolled by the monitor 109. For example, the driver 111 can providepulses of current to the emitter 104. In an embodiment, the driver 111drives the emitter 104 in a progressive fashion, such as in analternating manner. The driver 111 can drive the emitter 104 with aseries of pulses of about 1 milliwatt (mW) for some wavelengths that canpenetrate tissue relatively well and from about 40 mW to about 100 mWfor other wavelengths that tend to be significantly absorbed in tissue.A wide variety of other driving powers and driving methodologies can beused in various embodiments.

The detectors 106 can capture and measure optical radiation from themeasurement site 102. For example, the detectors 106 can capture andmeasure optical radiation transmitted from the emitter 104 that has beenattenuated or reflected from the tissue in the measurement site 102. Thedetectors 106 can output a detector signal 107 responsive to the opticalradiation captured or measured. The detectors 106 can be implementedusing one or more photodiodes, phototransistors, or the like. Althoughthe detectors 106 may be described as multiple detectors, in certainembodiments, the detectors 106 instead can be a single detector.

In one implementation, the detectors 106 can include one or morephotodiodes, such as at least one of the photodiodes described withrespect to FIG. 3 . The photodiode can detect optical radiation at bothvisible and near-infrared wavelengths and generate one or more detectorsignals responsive to the detected optical radiation. The one or moredetector signals can have a signal strength sufficient for the detectorsignal to be usable to determine measurement values for one or morephysiological parameters of the patient from the optical radiationdetected by the photodiode at both the visible and near-infraredwavelengths. For example, the photodiode can detect optical radiationhaving a wavelength of about 660 nm in the visible portion of theelectromagnetic spectrum and optical radiation having a wavelength ofabout 1000 nm in the near-infrared portion of the electromagneticspectrum and generate a detector signal based thereon.

One or more photodiodes of the detectors 106 can be defined in terms ofarea. In an embodiment, the area of one photodiode can be from about 1mm²-5 mm² (or higher) and capable of generating about 100 nanoamps (nA)or less of current resulting from measured optical radiation at fullscale. In addition to having its ordinary meaning, the phrase “at fullscale” can mean optical radiation saturation of a photodiode amplifier(not shown). The data collection system 100 can, for instance, measurefrom one photodiode an output current range of approximately about 2 nAto about 100 nA or more full scale. Various other sizes and types ofphotodiodes can be used with the embodiments of the present disclosure.

The detectors 106 can be arranged with different spatial configurations,such as to provide or not provide a variation of path lengths among atleast some of the detectors 106. Some of the detectors 106 can havesubstantially, or from the perspective of the processing algorithm,effectively, the same path length from the emitter 104. In one example,the detectors 106 can be arranged as is described in U.S. PatentApplication Publication No. 2010/0026995, filed Aug. 3, 2009, titled“Multi-stream Sensor for Noninvasive Measurement of Blood Constituents,”the disclosure of which is hereby incorporated by reference in itsentirety. In particular, the detectors can be arranged at least in partas described with respect to FIGS. 3E and 12A-12H of the aforementionedpublication, the associated paragraphs and figures of which are herebyincorporated specifically by reference.

The front-end interface 108 provides an interface that adapts the outputof the detectors 106, which is responsive to desired physiologicalparameters. For example, the front-end interface 108 can adapt a signal107 received from one or more of the detectors 106 into a form that canbe processed by the monitor 109, for example, by a signal processor 110in the monitor 109. The front-end interface 108 can also amplify currentfrom the detectors 106 at desired signal-to-noise ratios (SNRs), such asto a SNR about 80 decibels (dB), 100 dB, or 120 dB in order to measurevarious desired analytes. The front-end interface 108 can have itscomponents assembled in the sensor 101, in the monitor 109, inconnecting cabling (if used), combinations of the same, or the like. Thelocation of the front-end interface 108 can be chosen based on variousfactors including space desired for components, desired noise reductionsor limits, desired heat reductions or limits, and the like.

The front-end interface 108 can be coupled to the detectors 106 and tothe signal processor 110 using a bus, wire, electrical or optical cable,flex circuit, or some other form of signal connection. The front-endinterface 108 can also be at least partially integrated with variouscomponents, such as the detectors 106. For example, the front-endinterface 108 can include one or more integrated circuits that are onthe same circuit board as the detectors 106. Other configurations canalso be used.

The front-end interface 108 can be implemented using one or moreamplifiers, such as transimpedance amplifiers, that are coupled to oneor more analog to digital converters (ADCs) (which can be in the monitor109), such as a sigma-delta ADC. A transimpedance-based front-endinterface 108 can employ single-ended circuitry, differential circuitry,or a hybrid configuration. A transimpedance-based front-end interface108 can be useful for its sampling rate capability and freedom inmodulation/demodulation algorithms. For example, this type of front-endinterface 108 can advantageously facilitate the sampling of the ADCsbeing synchronized with the pulses emitted from the emitter 104.

The ADC or ADCs can provide one or more outputs into multiple channelsof digital information for processing by the signal processor 110 of themonitor 109. Each channel can correspond to a signal output from adetector 106.

As shown in FIG. 1 , the monitor 109 can include the signal processor110 and a user interface 112, such as a display. The monitor 109 canalso include optional outputs alone or in combination with the userinterface 112, such as a storage device 114 and a network interface 116.The signal processor 110 can include processing logic that determinesmeasurements for desired analytes, such as glucose, based on the signalsreceived from the detectors 106. The signal processor 110 can beimplemented using one or more microprocessors or subprocessors (e.g.,cores), digital signal processors, application specific integratedcircuits (ASICs), field programmable gate arrays (FPGAs), combinationsof the same, and the like.

The signal processor 110 can provide various signals that control theoperation of the sensor 101. For example, the signal processor 110 canprovide an emitter control signal to the driver 111. This control signalcan be useful in order to synchronize, minimize, or reduce jitter in thetiming of pulses emitted from the emitter 104. Accordingly, this controlsignal can be useful in order to cause optical radiation pulses emittedfrom the emitter 104 to follow a precise timing and consistent pattern.As also shown, an optional memory 113 can be included in the front-endinterface 108 or in the signal processor 110. This memory 113 can serveas a buffer or storage location for the front-end interface 108 or thesignal processor 110, among other uses.

The user interface 112 can provide an output, for example, on a display,for presentation to a user of the data collection system 100. The userinterface 112 can be implemented as a touch-screen display, an LCDdisplay, an organic LED display, or the like. In addition, the userinterface 112 can be manipulated to allow for measurement on thenon-dominant side of patient. For example, the user interface 112 caninclude a flip screen, a screen that can be moved from one side toanother on the monitor 109, or can include an ability to reorient itsdisplay indicia responsive to user input or device orientation. Inalternative embodiments, the data collection system 100 can be providedwithout a user interface 112 and can simply provide an output signal toa separate display or system.

A storage device 114 and a network interface 116 represent otheroptional output connections that can be included in the monitor 109. Thestorage device 114 can include any computer-readable medium, such as amemory device, hard disk storage, EEPROM, flash drive, or the like. Thevarious software or firmware applications can be stored in the storagedevice 114, which can be executed by the signal processor 110 or anotherprocessor of the monitor 109. The network interface 116 can be a serialbus port (RS-232/RS-485), a Universal Serial Bus (USB) port, an Ethernetport, a wireless interface (e.g., WiFi such as any 802.1x interface,including an internal wireless card), or other suitable communicationdevice(s) that allows the monitor 109 to communicate and share data withother devices. The monitor 109 can also include various other componentsnot shown, such as a microprocessor, graphics processor, or controllerto output the user interface 112, to control data communications, tocompute data trending, or to perform other operations.

Although not shown in the depicted embodiment, the data collectionsystem 100 can include various other components or can be configured indifferent ways. For example, the sensor 101 can have both the emitter104 and detectors 106 on the same side of the measurement site 102 anduse reflectance to measure analytes. The data collection system 100 canalso include a sensor that measures the power of optical radiationemitted from the emitter 104. Moreover, although the detectors 106 maybe initially constructed to include one of the photodiodes describedwith respect to FIG. 3 , the detectors 106 may also instead beretrofitted with one of the photodiodes described with respect to FIG. 3in some implementations.

FIG. 2 illustrates an example sensor operation process 200. The process200 illustrates an example operation of the sensor 101 and may beimplemented by the various components shown in the data collectionsystem 100. For convenience, the process 200 is described in the contextof the data collection system 100 but may instead be implemented byother systems described herein or other sensor systems not shown. Theprocess 200 provides one example approach by which the sensor 101 canemit visible and near-infrared optical radiation wavelengths and detectwith a photodiode, such as one of the photodiodes described with respectto FIG. 3 , the optical radiation after attenuation by tissue of apatient. Advantageously, in certain embodiments, the process 200 enablesthe sensor 101 to output from the photodiode a detector signalresponsive to both visible and near-infrared wavelengths afterattenuation by the tissue.

At block 205, the emitter 104 can receive a drive signal from the driver111. At block 210, the drive signal can cause the emitter 104 toirradiate tissue of a patient at wavelengths of visible opticalradiation and near-infrared optical radiation. At block 215, aphotodiode of the detectors 106 can detect the optical radiation afterattenuation by the tissue. At block 220, the photodiode of the detectors106 can generate one or more detector signals responsive to the detectedoptical radiation at the visible and near-infrared wavelengths. Forinstance, the photodiode can generate one signal responsive to thedetected optical radiation at the visible wavelength and another signalresponsive to the detected optical radiation at the near-infraredwavelength when the visible and near-infrared wavelengths are emitted atdifferent times, or the photodiode can output can output a combinedsignal responsive to the detected optical radiation at the visible andnear-infrared wavelengths when the visible and near-infrared wavelengthsare emitted at substantially the same time. At block 225, the sensor 101can output the one or more detector signals for processing by the signalprocessor 110 to determine measurement values for one or morephysiological parameters of the patient.

III. Example Photodiodes

FIG. 3 illustrates an example schematic diagram of a semiconductordevice 300. The semiconductor device 300 can, for instance, be part ofan integrated semiconductor structure including one or more othercomponents. The semiconductor device 300 includes a distal side metalcontact 302 and a proximal side metal contact 314. The semiconductordevice 300 further includes a semiconductor wafer 304, an absorptionregion 306, a detector window layer 308, a diffusion region 310, and adiffusion mask 312 that together can form a photodiode, such as aphotodiode usable as one of the detectors 106 of FIG. 1 . Opticalradiation can enter the photodiode through the detector window layer 308before passing to other layers of the photodiode, such as the absorptionregion 306. Although not illustrated, an anti-reflective coating can beapplied to the surface of the photodiode, such as the detector windowlayer 308, to increase the transmittance of the photodiode.

In one implementation, the distal side metal contact 302 can be ann-type region contact and the proximal side metal contact 314 can be ap-type region contact. The semiconductor wafer 304 can, for instance, bean n-type InP wafer, which includes indium and phosphorous. Theabsorption region 306 can, for instance, be (i) an n-type or undopedInGaAs absorption region, which includes indium, gallium, and arsenic,(ii) an n-type or undoped InAlGaAs absorption region, which includesindium, aluminum, gallium, and arsenic, or (iii) an n-type or undopedInGaAsP region, which includes indium, gallium, arsenic, andphosphorous. The diffusion region 310 can, for instance, be a diffusedregion that turns n-type or undoped material into a p-type region toform a p-n semiconductor junction in selected areas defined by thediffusion mask 312. The diffusion mask 312 can, for instance, be a SiNor SiO₂ diffusion mask. The photodiode, in one implementation, canaccordingly be an InGaAs PIN photodiode.

The detector window layer 308 can be a layer that is sufficiently thinso that the detector window layer 308 passes visible optical radiationfor detection by the photodiode and yet provides passivation of theabsorption region 306 and the diffusion region 310, which can be azinc-diffused P region, so that electron-hole pairs generated by thevisible optical radiation, including short-wavelength optical radiation,near the surface of the photodiode (for example, in the P-region) have alower recombination rate resulting in a quantum efficiency enhancementat visible wavelengths. For example, the detector window layer 308 canbe a layer having a thickness of less than about 150 nm, such as athickness ranging from about 25 nm to about 150 nm, from about 40 nm toabout 130 nm, from about 50 nm to about 100 nm, or from about 45 nm toabout 55 nm or a thickness of about 50 nm. Because the detector windowlayer 308 being thinner may result in more visible wavelengths passinginto the photodiode, the detector window layer 308 can be desirablyabout 50 nm in certain implementations. The detector window layer 308can be an epitaxially grown layer.

In one example, the detector window layer 308 can be an InP layer, whichincludes indium and phosphorous. The InP layer can have a bandgap ofabout 1.34 eV at 25° C. If the InP layer is about 400 nm thick, theexternal quantum efficiency at 660 nm can be about 8%. If the InP layermay be made thinner such as around 50 nm, the external quantumefficiency at 660 nm can be about 58%. Thinner layers, such as aboutwindow layers having a thickness of about 25 nm, can be made, but ifmade too thin, the microfabrication procedures used to make thephotodiode may, in some instances, slightly etch or oxide the windowlayers, leaving no or minimal window layer so that the surface of theInGaAs or InAlGaAs photodiode may be unpassivated and have a lowerquantum efficiency for visible wavelengths (for example, shorterwavelengths) due to enhanced recombination of photogenerated carriers inthe layer at the unpassivated surface. There can thus exist an optimumInP layer thickness between 0 nm and about 50 nm for such devices, inparticular implementations.

As another example, the detector window layer 308 can be an InAlAslayer, which includes indium, aluminum, and arsenic, which can either beof a composition whose atomic crystal lattice constant islattice-matched or lattice mismatched to the absorption region 306 andsemiconductor wafer 304. Advantageously, in certain embodiments, theInAlAs layer can be desirably thin to efficiently pass visible opticalradiation for detection by the photodiode, similar to the InP layerexample explained in the preceding paragraph. In one implementation, theInAlAs layer can be formed of a composition of In_(0.52)Al_(0.48)As thathas a bandgap of about 1.52 eV at 25° C. and is lattice-matched to thesemiconductor wafer 304. It has been determined that theIn_(0.52)Al_(0.48)As layer can begin to strongly attenuate opticalradiation at wavelengths shorter than about 817 nm as compared to anattenuation wavelength of about 920 nm at 25° C. for an InP layer andtherefore can result in a relatively higher external quantum efficiency.In another implementation, the InAlAs layer can be formed of acomposition of In_(0.46)Al_(0.54)As that has a larger bandgap of about1.68 eV and is not lattice-matched to the semiconductor wafer 304. Ithas been determined that the In_(0.46)Al_(0.54)As layer can begin tostrongly attenuate optical radiation at wavelengths shorter than about739 nm and the external quantum efficiency for the photodiode with theIn_(0.46)Al_(0.54)As layer may be about 78% at a wavelength about 660nm. Because the detector window layer 308 having a higher bandgap canresult in more visible optical radiation passing into the photodiode,the detector window layer 308 can be desirably composed ofIn_(0.46)Al_(0.54)As in certain implementations. Although the InAlAscomposition may be lattice-mismatched to the crystal lattice constant ofone or more of the underlying layers, is the layer can be generallysufficiently thin so that the layer may be strained to fit on theunderlying crystal lattice without generation of dislocation defects, acondition that can be known as pseudomorphic growth. The following Table1 summarizes some measured data for the above-referenced window layersof a similar photodiode structure and compares them to a model resultfor a photodiode structure with a window layer composed of InP with athickness of 400 nm.

TABLE 1 External Quantum Layer Thick- Band- Lattice- Efficiency at 660nm Composition ness gap Matched Wavelength InP 400 nm 1.34 eV Yes  8%InP  50 nm 1.34 eV Yes 58% In_(0.46)Al_(0.54)As  50 nm 1.68 eV No 78%

FIG. 4 illustrates a graph 400 of quantum efficiency versus opticalradiation wavelength for various example photodiodes. The graph 400illustrates that the teachings of this disclosure can enable theconstruction of a photodiode that has a relatively higher quantumefficiency at both visible and near-infrared wavelengths compared to atraditional photodiode. As used herein, external quantum efficiency, inaddition to having its ordinary meaning, can refer to the ratio of thenumber of charge carriers collected to the number of photons of a givenenergy shining on the photodiode from outside the photodiode. Theexternal quantum efficiency, for instance, can be proportional to theamount of current that a photodiode produces when irradiated by photonsof a particular wavelength.

The curve 402 depicts a model relationship between external quantumefficiency versus optical radiation wavelength for a traditionalphotodiode formed from the semiconductor device 300 where the absorptionregion 306 is an n-type InAlGaAs absorption region and the detectorwindow layer 308 has a thickness of about 400 nm and is an InP layer.The curve 404 depicts the measured relationship between external quantumefficiency versus optical radiation wavelength for a photodiode formedfrom the semiconductor device 300 where the absorption region 306 is ann-type InAlGaAs absorption region and the detector window layer 308 hasa thickness of about 50 nm and is an InP layer. The curve 406 depictsthe measured relationship between external quantum efficiency versusoptical radiation wavelength for a photodiode formed from thesemiconductor device 300 where the absorption region 306 is an n-typeInAlGaAs absorption region and the detector window layer 308 has athickness of about 50 nm and is a lattice-mismatchedIn_(0.46)Al_(0.54)As layer.

As can be seen from curves 404 and 406 of the graph 400, the quantumefficiency of an enhanced photodiode constructed in accordance withteachings of this disclosure can notably have an external quantumefficiency of greater than about 30% (such as an external quantumefficiency ranging from about 30% to about 90%, from about 50% to about85%, or from about 60% to about 80% or an external quantum efficiency ofabout 50%, about 60%, about 70%, about 80% or about 90%) at wavelengthsranging from about 450 nm to 850 nm. Such an enhanced photodiode canaccordingly be used, for instance, to detect optical radiation atwavelengths ranging from about 450 nm to about 850 nm, as well as fromabout 850 nm to about 1400 nm or 1430 nm.

Although the curves 402, 404, and 406 depict the quantum efficiencyversus optical radiation wavelength for a photodiode where theabsorption region 306 is an n-type InAlGaAs absorption region, theabsorption region 306 may in some cases instead be an n-type InGaAsabsorption region as mentioned previously. If the curves 402, 404, and406 were depicted for photodiodes including the n-type InGaAs absorptionregion, the responsiveness of the photodiodes would further extend toabout 1700 nm rather than about 1430 nm as illustrated in the graph 400.Therefore, in such implementations, an enhanced photodiode can be used,for instance, to detect optical radiation at wavelengths ranging fromabout 450 nm to about 850 nm, as well as from about 850 nm to about 1700nm. In such implementations, the enhanced photodiode can, for instance,have an external quantum efficiency of greater than about 70% (such asan external quantum efficiency ranging from about 70% to about 95%, fromabout 80% to about 95%, from about 85% to about 95%, or from about 90%to about 95% or an external quantum efficiency of about 70%, about 80%,about 85%, about 90%, or about 95%) at wavelengths ranging from about1400 nm to 1700 nm.

As illustrated by the graph 400, an enhanced photodiode having theperformance characteristics of the curve 404 can have an externalquantum efficiency of about 9% at 400 nm, 28% at 450 nm, 41% at 500 nm,49% at 550 nm, 52% at 600 nm, 55% at 650 nm, 58% at 700 nm, 62% at 750nm, 65% at 800 nm, 71% at 850 nm, 75% at 900 nm, 82% at 950 nm, 85% at1000 nm, 89% at 1050 nm, 89% at 1100 nm, 92% at 1150 nm, 92% at 1200 nm,92% at 1250 nm, 92% at 1300 nm, 92% at 1350 nm, 85% at 1400 nm, and 5%at 1450 nm. In addition, as illustrated by the graph 400, an enhancedphotodiode having the performance characteristics of the curve 406 canhave an external quantum efficiency of about 12% at 400 nm, 40% at 450nm, 65% at 500 nm, 75% at 550 nm, 77% at 600 nm, 78% at 650 nm, 80% at700 nm, 82% at 750 nm, 86% at 800 nm, 88% at 850 nm, 90% at 900 nm, 91%at 950 nm, 92% at 1000 nm, 94% at 1050 nm, 93% at 1100 nm, 96% at 1150nm, 96% at 1200 nm, 95% at 1250 nm, 94% at 1300 nm, 92% at 1350 nm, 85%at 1400 nm, and 10% at 1450 nm. Moreover, an enhanced photodiodeconstructed in accordance with the teachings of this disclosure can thushave an external quantum efficiency of at least the external quantumefficiency of the curve 404 or the curve 406 at the various wavelengthsillustrated in FIG. 4 , as well as at the additional range ofwavelengths from about 1400 nm to 1700 nm as described herein.Furthermore, an enhanced photodiode constructed in accordance with theteachings of this disclosure can thus have an external quantumefficiency of at least 10% to 30% (for example, 10%, 15%, 20%, 25%, or30%) at wavelengths ranging from 450 nm to 1400 nm, at least 10% to 65%(for example, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, or65%) at wavelengths ranging from 500 nm to 1400 nm, at least 10% to 75%(for example, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%,65%, 70%, or 75%) at wavelengths ranging from 550 nm to 1400 nm, atleast 10% to 75% (for example, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%,50%, 55%, 60%, 65%, 70%, or 75%) at wavelengths ranging from 600 nm to1400 nm, at least 10% to 78% (for example, 10%, 15%, 20%, 25%, 30%, 35%,40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, or 78%) at wavelengths rangingfrom 650 nm to 1400 nm, at least 15% to 80% (for example, 15%, 20%, 25%,30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, or 80%) at wavelengthsranging from 700 nm to 1400 nm, at least 20% to 80% (for example, 20%,25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, or 80%) atwavelengths ranging from 750 nm to 1400 nm, at least 25% to 85% (forexample, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, or85%) at wavelengths ranging from 800 nm to 1400 nm, at least 30% to 85%(for example, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, or85%) at wavelengths ranging from 850 nm to 1400 nm, at least 55% to 85%(for example, 55%, 60%, 65%, 70%, 75%, 80%, or 85%) at wavelengthsranging from 900 nm to 1400 nm, at least 85% at wavelengths ranging from950 nm to 1400 nm, or at least 90% at wavelengths ranging from 900 nm to1350 nm.

As illustrated by the graph 400, an enhanced photodiode constructed inaccordance with the teachings of this disclosure can have an externalquantum efficiency ranging at least from about 9% to 12% at 400 nm, 28%to 40% at 450 nm, 41% to 65% at 500 nm, 49% to 75% at 550 nm, 52% to 77%at 600 nm, 55% to 78% at 650 nm, 58% to 80% at 700 nm, 62% to 82% at 750nm, 65% to 86% at 800 nm, 71% to 88% at 850 nm, 75% to 90% at 900 nm,82% to 91% at 950 nm, 85% to 92% at 1000 nm, 89% to 94% at 1050 nm, 89%to 93% at 1100 nm, 92% to 96% at 1150 nm, 92% to 96% at 1200 nm, 92% to95% at 1250 nm, 92% to 94% at 1300 nm, 92% to 92% at 1350 nm, 85% to 85%at 1400 nm, and 5% to 10% at 1450 nm.

In some embodiments, when a photodiode has an external quantumefficiency at a particular wavelength that is below a threshold quantumefficiency level, an output current generated by the photodiode whenirradiated by photons of the particular wavelength can be sufficientlylow such that the photodiode may be considered to not detect theparticular wavelength. This can, in some instances, be because theoutput current generated by the photodiode when irradiated by photons ofthe particular wavelength may be insufficient for use in confidentlydetermining that the photodiode detected the particular wavelength. Thethreshold quantum efficiency level can vary, in certain embodiments,based at least on a system design in which the photodiode is used. Forexample, in certain medical device applications, such as in some examplenon-invasive sensor detector applications, the threshold quantumefficiency level can be about 30%, about 25%, about 20%, about 15%, orabout 10%, such that when a photodiode detects particular wavelengthsfor which the photodiode has an external quantum efficiency below thethreshold quantum efficiency level, the output current provided by thephotodiode may be insufficient for the non-invasive sensor toconfidently determine that the photodiode detected the particularwavelengths. Accordingly, in some instances, the photodiode may not beused to detect wavelengths for which the photodiode has an externalquantum efficiency below the threshold quantum efficiency level, or theoutput current from the photodiode may be discarded as not providingusable information or information of sufficient quality if the outputcurrent is below a threshold current corresponding to the thresholdquantum efficiency level.

Moreover, although some applications of the photodiode of thesemiconductor device 300 are described in the context of a non-invasivesensor, the photodiode can be useful in numerous other applications. Forexample, the photodiode can be part of a spectrometer in industrial ormanufacturing applications (for instance, in applications related toplastics, petroleum, chemical, or the like) and used to detect a broadrange of electromagnetic radiation for detecting a spectrum ofelectromagnetic radiation. As another example, the photodiode can bepart of a non-contact temperature measurement system and used to detecta broad range of electromagnetic radiation to determine a detectedtemperature. As a further example, the photodiode can be part of a flamemonitoring or control system and used to detect one or morecharacteristics of a flame from the detected broad spectrum ofelectromagnetic radiation. Moreover, the photodiode can be part of adiode laser monitoring system (for instance, for telecommunications orlidar applications) and used to detect a broad range of electromagneticradiation from one or more lasers.

IV. Terminology

Many other variations than those described herein will be apparent fromthis disclosure. For example, depending on the embodiment, certain acts,events, or functions of any of the algorithms described herein can beperformed in a different sequence, can be added, merged, or left outaltogether (e.g., not all described acts or events are necessary for thepractice of the algorithms). Moreover, in certain embodiments, acts orevents can be performed concurrently, e.g., through multi-threadedprocessing, interrupt processing, or multiple processors or processorcores or on other parallel architectures, rather than sequentially. Inaddition, different tasks or processes can be performed by differentmachines or computing systems that can function together.

The various illustrative logical blocks, modules, and algorithm stepsdescribed in connection with the embodiments disclosed herein can beimplemented as electronic hardware, computer software, or combinationsof both. To clearly illustrate this interchangeability of hardware andsoftware, various illustrative components, blocks, modules, and stepshave been described above generally in terms of their functionality.Whether such functionality is implemented as hardware or softwaredepends upon the particular application and design constraints imposedon the overall system. The described functionality can be implemented invarying ways for each particular application, but such implementationdecisions should not be interpreted as causing a departure from thescope of the disclosure.

The various illustrative logical blocks and modules described inconnection with the embodiments disclosed herein can be implemented orperformed by a machine, such as a general purpose processor, a digitalsignal processor (DSP), an application specific integrated circuit(ASIC), a field programmable gate array (FPGA) or other programmablelogic device, discrete gate or transistor logic, discrete hardwarecomponents, or any combination thereof designed to perform the functionsdescribed herein. A general purpose processor can be a microprocessor,but in the alternative, the processor can be a controller,microcontroller, or state machine, combinations of the same, or thelike. A processor can include electrical circuitry configured to processcomputer-executable instructions. In another embodiment, a processorincludes an FPGA or other programmable device that performs logicoperations without processing computer-executable instructions. Aprocessor can also be implemented as a combination of computing devices,e.g., a combination of a DSP and a microprocessor, a plurality ofmicroprocessors, one or more microprocessors in conjunction with a DSPcore, or any other such configuration. A computing environment caninclude any type of computer system, including, but not limited to, acomputer system based on a microprocessor, a mainframe computer, adigital signal processor, a portable computing device, a devicecontroller, or a computational engine within an appliance, to name afew.

The steps of a method, process, or algorithm described in connectionwith the embodiments disclosed herein can be embodied directly inhardware, in a software module stored in one or more memory devices andexecuted by one or more processors, or in a combination of the two. Asoftware module can reside in RAM memory, flash memory, ROM memory,EPROM memory, EEPROM memory, registers, hard disk, a removable disk, aCD-ROM, or any other form of non-transitory computer-readable storagemedium, media, or physical computer storage known in the art. An examplestorage medium can be coupled to the processor such that the processorcan read information from, and write information to, the storage medium.In the alternative, the storage medium can be integral to the processor.The storage medium can be volatile or nonvolatile. The processor and thestorage medium can reside in an ASIC.

Conditional language used herein, such as, among others, “can,” “might,”“may,” “e.g.,” and the like, unless specifically stated otherwise, orotherwise understood within the context as used, is generally intendedto convey that certain embodiments include, while other embodiments donot include, certain features, elements or states. Thus, suchconditional language is not generally intended to imply that features,elements or states are in any way required for one or more embodimentsor that one or more embodiments necessarily include logic for deciding,with or without author input or prompting, whether these features,elements or states are included or are to be performed in any particularembodiment. The terms “comprising,” “including,” “having,” and the likeare synonymous and are used inclusively, in an open-ended fashion, anddo not exclude additional elements, features, acts, operations, and soforth. Also, the term “or” is used in its inclusive sense (and not inits exclusive sense) so that when used, for example, to connect a listof elements, the term “or” means one, some, or all of the elements inthe list. Further, the term “each,” as used herein, in addition tohaving its ordinary meaning, can mean any subset of a set of elements towhich the term “each” is applied.

Terms such as “substantially,” “about,” “approximately” or the like asused in referring to a relationship between two objects is intended toreflect not only an exact relationship but also variances in thatrelationship that may be due to various factors such as the effects ofenvironmental conditions, common error tolerances, manufacturingvariances, or the like. It should further be understood that althoughsome values or other relationships may be expressed herein without amodifier, these values or other relationships may also be exact or mayinclude a degree of variation due to various factors such as the effectsof environmental conditions, common error tolerances, or the like. Forexample, when referring to wavelengths of electromagnetic radiation,about a specified wavelength can, in some contexts, refer to awavelength variation of around less than 1% (such as a variation of 1%,0.8%, 0.5%, or 0.3%) from the specified wavelength. Accordingly, anabout 660 nm wavelength can refer to 660 nm±6 nm, 660 nm±5 nm, 660 nm±3nm, or 660 nm±2 nm. As another example, when referring to a thickness ofa layer, about a specified thickness can, in some contexts, refer to athickness variation of around less than 5% (such as a variation of 5%,3%, 2%, 1%, or 0.1%) from the specified thickness. Accordingly, an about50 nm thickness can refer to 50 nm±2.5 nm, 50 nm±1.5 nm, 50 nm±1 nm, or50 nm±0.5 nm, or 50 nm±0.05 nm. As a further example, when referring toan eV of a bandgap, about a specified eV can, in some contexts, refer toan eV variation of around less than 2% (such as a variation of 2%, 1.5%,1%, or 0.5%) from the specified eV. Accordingly, an about 1.52 eVbandgap can refer to 1.52 eV±0.03 eV, 1.52 eV±0.023 eV, 1.52 eV±0.015eV, or 1.52 eV±0.008 eV. In another example, when referring to anexternal quantum efficiency of a layer, about a specified externalquantum efficiency percentage can, in some contexts, refer to anexternal quantum efficiency percentage variation of around less than 3%(such as a variation of 3%, 2%, 1%, or 0.5%) from the specified externalquantum efficiency percentage. Accordingly, an about 58% externalquantum efficiency can refer to 58%±3%, 58%±2%, 58%±1%, or 58%±0.5%.

Disjunctive language such as the phrase “at least one of X, Y and Z,”unless specifically stated otherwise, is to be understood with thecontext as used in general to convey that an item, term, etc. may beeither X, Y, or Z, or a combination thereof. Thus, such conjunctivelanguage is not generally intended to imply that certain embodimentsrequire at least one of X, at least one of Y and at least one of Z toeach be present.

Unless otherwise explicitly stated, articles such as “a” or “an” shouldgenerally be interpreted to include one or more described items.Accordingly, phrases such as “a device configured to” are intended toinclude one or more recited devices. Such one or more recited devicescan also be collectively configured to carry out the stated recitations.For example, “a processor configured to carry out recitations A, B andC” can include a first processor configured to carry out recitation Aworking in conjunction with a second processor configured to carry outrecitations B and C.

While the above detailed description has shown, described, and pointedout novel features as applied to various embodiments, it will beunderstood that various omissions, substitutions, and changes in theform and details of the devices or algorithms illustrated can be madewithout departing from the spirit of the disclosure. As will berecognized, certain embodiments described herein can be embodied withina form that does not provide all of the features and benefits set forthherein, as some features can be used or practiced separately fromothers.

What is claimed is:
 1. A physiological sensor for measuringphysiological parameters of a monitored patient, the physiologicalsensor comprising: a detector configured to generate a detector signalresponsive to optical radiation incident on the detector afterattenuation by a tissue of a patient, wherein the detector comprises awindow layer, a diffusion region, an absorption region, and asemiconductor wafer, the absorption region being between the windowlayer and the semiconductor wafer, wherein the diffusion region is ap-type region and part of the window layer and the absorption region,and wherein the semiconductor wafer is a n-type region.
 2. Thephysiological sensor of claim 1, wherein the absorption region isadjacent to the semiconductor wafer and is an undoped region or then-type region.
 3. The physiological sensor of claim 1, wherein thewindow layer is the p-type region.
 4. The physiological sensor of claim1, wherein the window layer and the diffusion region form at least aportion of an exterior surface of the detector.
 5. The physiologicalsensor of claim 1, wherein the window layer and the diffusion region areconfigured to receive the optical radiation prior to the absorptionregion and the semiconductor wafer receiving the optical radiation. 6.The physiological sensor of claim 1, wherein the absorption region isconfigured to receive the optical radiation prior to the semiconductorwafer receiving the optical radiation.
 7. The physiological sensor ofclaim 1, further comprising an anti-reflective coating on the windowlayer.
 8. The physiological sensor of claim 1, further comprising adiffusion mask on the window layer, the diffusion mask comprisingsilicon.
 9. The physiological sensor of claim 1, wherein the diffusionregion is zinc-diffused.
 10. The physiological sensor of claim 1,further comprising: a first metal contact adjacent to the semiconductorwafer; and a second metal contact adjacent to the window layer.
 11. Thephysiological sensor of claim 10, wherein the first metal contact is then-type region, and the second metal contact is the p-type region. 12.The physiological sensor of claim 1, wherein the absorption regioncomprises indium, gallium, and arsenic, and the window layer comprisesindium, aluminum, and arsenic.
 13. The physiological sensor of claim 1,wherein the absorption region comprises indium, gallium, and arsenic,and the window layer comprises indium and phosphorus.
 14. Thephysiological sensor of claim 1, wherein the window layer is not latticematched to the semiconductor wafer, and the window layer is not latticematched to the absorption region.
 15. The physiological sensor of claim1, wherein the window layer is lattice matched to the semiconductorwafer.
 16. The physiological sensor of claim 1, wherein the detector hasa surface area of at least 5 mm² over which the detector is configuredto detect the optical radiation after attenuation by the tissue.
 17. Thephysiological sensor of claim 1, wherein the window layer has a bandgapranging from about 1.34 eV to about 1.9 eV at 25° C.
 18. Thephysiological sensor of claim 1, wherein the detector is configured togenerate the detector signal to have a current of at least 100 nA. 19.The physiological sensor of claim 1, further comprising: an emitterconfigured to emit the optical radiation at a visible wavelength and anear-infrared wavelength; and a sensor housing configured to support theemitter and the detector.
 20. The physiological sensor of claim 19, incombination with a patient monitor configured to determine a measurementvalue for a physiological parameter from the detector signal, thephysiological parameter comprising a blood analyte.